1. Field of the Invention
The present invention relates to a binding cord for a motor. In particular, the present invention relates to a binding cord for a motor that is suitable for binding of motor wires of an electric vehicle.
2. Description of Related Art
It has conventionally been required to reduce the harmful substances in the exhaust gas of vehicles while at the same time increasing the fuel efficiency of the vehicles. In recent years, there has been a growing demand to reduce the burden on the global environment. Under these circumstances, the research and development of electric vehicles are carried out actively. For example, the following electric vehicles are being developed at present: a pure electric vehicle (PEV) equipped with a high-capacity secondary battery; a hybrid electric vehicle (HEV) equipped with, e.g., a combination of a gasoline engine and a high-power secondary battery; a fuel cell vehicle (FCV) equipped with a fuel cell; and a fuel cell hybrid electric vehicle (FCHEV) equipped with, e.g., a combination of a fuel cell and a high-power secondary battery. In each case, high-efficiency motors need to be developed. Such motors are used for driving, electric power generation, charging, etc. The motors are strongly required to ensure not only high efficiency, but also stable performance in terms of driving stability. In particular, the motors for electric vehicles should have excellent high temperature oil resistance as compared to general motors for vehicles. It is necessary to place the motors for electric vehicles in an automatic transmission fluid (ATF) to improve the efficiency. Since the ATF may reach a high temperature, the motors should have high heat resistance in the ATF. Moreover, there has also been a demand to develop materials with uniform properties for components of the motors.
When a stator of a motor uses wire-wound coils such as wave winding coils and lap winding coils, the ends of the coils need to be bound with a binding string (binding cord) to prevent the wires from spreading apart, to make the coils compact, and to ensure the insulation distance. The binding cord for a coil is required to have, e.g., oil resistance, heat resistance, strength, and cost effectiveness. The fiber materials include aramid fibers, PPS fibers, and glass fibers. With mass production, the binding cord is generally tied around the coils by machine at present. In the mechanical binding, a space into which a machine is inserted should be provided between the end face of the stator and the ends of the coils. In the manual binding, such a space is not necessary, so that the height of the ends of the coils can be made as low as possible. This can suppress the volume of the coil end portion, and thus can reduce the weight of the motor and the winding resistance. Therefore, the manual binding has the advantage of improving the performance of the motor.
The applicant proposed in Patent Document 1 that filament yarns or spun yarns of synthetic fibers are braided to form a binding cord for a motor. Patent Documents 2 to 3 disclose that filament yarns of synthetic fibers are air interlaced with each other to form a braid. The applicant proposed in Patent Document 4 that a flat tubular binding cord is composed of 8 or more strands of multifilament yarns having high temperature oil resistance. This binding cord has high heat resistance, excellent high temperature oil resistance, flexibility, and good usability. Therefore, the binding cord is highly useful in the mechanical binding. The applicant proposed in Patent Document 5 that spun yarns of synthetic fibers are braided to form a binding cord for a motor.